Electrical connectors of the flat plug and receptacle type are commonly used in electrical circuits associated with machinery, especially automotive vehicles, in which they are subjected to vibrations and other forces. In such applications, the electrical connector must afford good electrical contact and, at the same time, it must provide a releaseable connection between the flat plug and the receptacle.
Lockable flat plug receptacles are known in the prior art which are formed from sheet metal with a substantially duct-shaped plug receiver with a bottom wall and with side walls which are arched-over the bottom wall to receive the flat plug. A tongue which is unitary with the bottom wall and which is bent back into the inside of the receiver is provided with a tang which is adapted to coact with an opening in the flat plug to secure it against being pulled out of the receptacle. In such receptacles, it is known to provide a releasing means on the free end of the tongue which is operable to bend the tongue away from the flat plug to release the plug and allow it to be removed from the receptacle.
A variety of forms of lockable electrical flat plug receptacles have been proposed. A connector with a lockable receptacle which is releaseable by being pushed inside a case is disclosed in U.S. Pat. Nos. 3,796,987 and 3,976,348 and from German published patent application Nos. 2,518,003 and 2,924,596. In this prior art, the tongues extend backward beyond the receiver and are bent at an angle to form a releasing means.